1. Field of the Invention
The present invention relates to an image pick-up apparatus and an endoscope apparatus having an image pick-up device whose amplification rate can be varied therein.
2. Description of the Related Art
Currently, an electronic endoscope is widely used for various therapeutic treatment processing which is performed by observing the trachea such as the lung or the gastrointestinal tract such as the esophagus, stomach, small intestine, and large intestine by inserting a scope in the body cavity with a treatment tool that is inserted in a treatment tool channel if necessary.
Recently, the auto-fluorescent observation is executed by using the auto-fluorescence of the living body in addition to the normal observation in which a color image is displayed on a monitor like viewing by naked eyes. In the auto-fluorescent observation, the diagnosis is performed by using the feature that the auto-fluorescent spectrums outputted from the living-body tissue are varied between the normal mucous membrane and the tumor upon hitting the ultraviolet to blue excitation light to the living-body tissue (refer to, e.g., Japanese Unexamined Patent Application Publication No. 2002-336196). Different colors are assigned to the auto-fluorescent image and the resultant image which are displayed on the monitor together with a reflecting-light image which is reflected and is returned from the living-body tissue, thereby clearly recognizing the lesion.
Since the fluorescent light is weak, an image pick-up device with high sensitivity is necessary for the image pick-up operation. For example, U.S. Pat. Publication No. 5,337,340 suggests one of the image pick-up devices with high sensitivity, comprising a CCD whose amplification rate therein is controlled by inputting a control pulse externally from the image pick-up device. The CCD comprises a CMD (Charge Multiplying Device) arranged therein which can increase the charges by using the ionization. The CMD can be arranged to each pixel, thereby performing the amplification every pixel, and further can be arranged to transfer channels, thereby performing the amplification every transfer line. Advantageously, the variation in amplification rate every pixel in the CMD does not influence and thus the CMD is put into practical use, in which the CMD is arranged to the transfer channel. The amplification rate of the image pick-up device having the CMD in the transfer channel is controlled by changing the amplitude of the control pulse inputted to the CMD (CMD gate pulse). The amplification is-performed in the CCD using the CMD before reading the charges in the CCD. Therefore, there is a merit that the influence of reading noises is suppressed, as compared with the amplification out of the CCD and the image with an excessively high S/N ratio is obtained. The image pick-up operation is possible with high sensitivity and is suitable to the weak light.